This invention relates to a hydraulic fluid circuit of a hydraulic shovel.
As shown in FIG. 1, a prior art loading shovel includes a lower travel member 1, a swing 2, a boom 3, an arm 4, a bucket 5, a hydraulic boom cylinder 6, a hydraulic arm cylinder 7, and a hydraulic bucket cylinder 8, for driving the front loading portion including the boom 3, arm 4, and bucket 5.
As shown in FIG. 2, a prior art hydraulic fluid circuit for the loading shovel includes hydraulic pumps 9, 10 and directional control valve groups generally designated by the reference numerals 11, 12 respectively connected to the hydraulic pumps 9, 10. The directional control valve groups 11, 12 are of the four valve type of the same construction, with one valve group 11 comprising a boom control valve 13, a left travel control valve 35, an arm control valve 15, and a swing control valve 36, and the other group 12 comprising a boom control valve 14, a right travel control valve 37, a bucket control valve 16 and a reserve control valve 38.
The hydraulic circuit further includes a pilot pump, a relief valve 18, a control pilot valve 19 for the boom control valves 13, 14 a control pilot valve 20 for the arm control valve 15, and a control pilot valve 21 for the bucket control valve 16. Left and right travel control valves 35, 37, forming a control circuit, are connected to the hydraulic fluid circuit in a known manner not shown in FIG. 2.
In the hydraulic fluid circuit shown in FIG. 2, the hydraulic cylinders 6-8 are shortened when the pilot valves 19-21 are each brought to position A, and lengthened when they are each brought to position B.
When the pilot valve 19 is actuated to operate the boom cylinder 6, the boom cylinder 6 receives a supply of hydraulic fluid from the hydraulic pumps 9, 10 via the two control valves 13, 14, so that the boom cylinder 6 operates at high speed. However, when the pilot valve 20 is actuated to operate the arm cylinder 7, it is only from the hydraulic pump 9 that the hydraulic fluid is supplied to the arm cylinder 7 via the single directional control valve 15. Thus, the arm cylinder 7 operates at low speed, and the hydraulic pump 10 is not utilized to actuate the arm cylinder 7. Likewise, when the bucket cylinder 8 is operated, hydraulic fluid only from the hydraulic pump 10 is supplied to the bucket cylinder 7 via the single directional control valve 16, so that the bucket cylinder 8 operates at low speed and the hydraulic pump 9 is not utilized to actuate the bucket cylinder 8. Thus, on might consider that if the arm cylinder 7 and the bucket cylinder 8 are operated by additionally providing a bucket control valve and an arm control valve to the directional control valve groups 11, 12, respectively, pressure fluid could be supplied from the hydraulic pumps 9, 10 to the arm cylinder 7 and bucket cylinder 8. However, when this is the case, even if the reserve control valve 38 of the directional control valve group 12 is utilized as an additional arm control valve, it would be necessary to provide an additional bucket control valve to the directional control valve group 11. This would create the need to manufacture a new five valve type directional control valve group, resulting in an increase in production cost and ending the advantage of using the two directional control valve groups 11, 12 of the same construction. Moreover, an increase in the size of the control valve group 11 raises the problem of securing necessary space for this purpose.